This invention relates to a novel and improved combination weighing method and, more particularly, to a highly accurate combination selecting method applicable to a conventional combination weighing machine.
As is well known in the art, in a combination weighing machine, batches of product are weighed by a plurality of weighing units and the resultant weight values are combined to select from the resultant combinations a combination whose total weight is, for example, nearest to a predetermined target value. The batches of product corresponding to the selected combination is then unloaded. In an automatic combination weighing machine, a combination arithmetic and delivery cycle of this type is repeated. In order to improve machine efficiency, a so-called "double-shift" system is generally used, in which the combination arithmetic operation is commenced using only the weighing weighing units not selected in the preceding cycle. Such a system is disclosed, for example, in U.S. Pat. Nos. 4,385,671; 4,470,166 and 4,589,506 and Japanese opened patent specification No. 58-2621, the latter of which discloses such a system as shown in FIG. 1 of the present application, in which batches of product are delivered successively at short time intervals and diverted alternately into a pair of collection chutes for preventing their intermixing.
In this double-shift system, it has not been believed possible to improve the combination accuracy using a fixed number of weight values to be combined, since the combination selected in each cycle is nearest to the target value and this automatically results in the minimum mean deviation of the total weights of the selected combinations with respect to the target weight. Accordingly, it has been a general practice of the prior art for improving the combination accuracy to increase the number of weight values which can participate in the combination arithmetic by increasing the total number of weighing units and/or providing auxiliary hoppers. However, increasing the number of structural components renders the device more complicated, larger and more costly.